The disclosed invention is advantageously utilized to provide automatic control for achieving the optimal distribution of electric power within an electrostatic precipitator while maintaining acceptable environmental standards. An electrostatic precipitator utilizes high voltage electrodes to charge particulate matter in a high voltage or corona field. The charging voltage is further used to collect the charged particles on the oppositely charged electrodes of the precipitator. Periodic rapping of the electrodes is usually required to loosen the particulates and to thereby maintain the operating efficiency of the precipitator.
A typical electrostatic precipitator utilizes a plurality of paired oppositely charged electrodes disposed, at least in part, in the flue gas flow path. The electrodes are usually arranged in groups or fields. A transformer-recitifer (T-R) set provides power to a field, to several fields or to a portion of a field and is used to generate the corona power between the paired electrodes.
Field voltage, hence corona power, is regulated and controlled by the amount of current provided by a regulator to each T-R set. Dedicated control for each T-R set is normally provided. Dedicated control of each T-R set permits independent energization of each field in order to enhance the collection of the particulates. Additionally, independent energization of the fields permits profiling of the precipitator fields in order to optimize the collection of particulates by the various fields.
Prior art control techniques have frequently sought to maintain the field voltage at a high voltage that is close to the "sparking limit" of the field. The field voltage is thereby maintained at maximun power regardless of whether maximum power is necessary. Consequently, the extra power is wasted and needlessly increases the operating costs of the precipitator. Experience has shown that the power requirement is related to many factors, such as: flue gas flow, particulate loading and the temperature of the flue gas, among others.
The continuing increase in the cost of electricity, which is utilized to energize the individual fields of the precipitator, has brought forth a need to optimize power consumption while still attaining particulate emission levels at their design limits and as mandated by environmental regulations. Manual adjustment of the individual T-R sets can provide some power reduction but control by this means is extremely inexact.
Reese, et al., U.S. Pat. No. 4,284,417, discloses one method for controlling the electric power supplied to an electrostatic precipitator. Reese discloses the utilization of an opacity transducer adapted for monitoring the opacity of the flue gas exiting the precipitator. Reese discloses that the power to the precipitator may be regulated so that the opacity remains just below the established environmental guidelines. Reese fails to realize, however, that major reductions in opacity are achieveable for minor increases in corona power to a point of optimum power utilization. Consequently, relatively minor increases in power can provide a cleaner environment at a reasonable cost. Reese attempts to achieve an opacity level just short of that required rather than attempting to remove the maximum amount of particulates from the stream. Reese fails to appreciate the downstream effects and costs occasioned by the large quantity of particulates remaining in the flue gas stream.